1. Field of the Invention
This invention relates to improvements in the distance measuring device for a camera capable of measuring the distances of a plurality of objects within a target area as defined by a picture frame of the camera.
2. Description of the Prior Art
In conventional cameras, to automatically detect the in-focus condition, the so-called range finder for producing information representing the distance from the camera to an object to be photographed is responsive to the object only when its image lies near or at the central area of the picture frame of the camera. For a composition in which the image of a subject of principal photographic interest is put in the margin of the picture frame, the photographer first needs to preliminarily align the camera so that the subject image is in the range finder mark located at the center of the view finder to measure the distance of the subject, and then, while holding that measured distance information, to change the camera alignment so that the subject image reaches a desired location in the margin of the view finder before a camera release is actuated, in other words, to pre-focusing.
For the beginner, however, this pre-focusing technique is difficult to apprehend. Also, since the performance of the automatic focusing devices has been greatly improved today, most of the out-of-focus photographs are taken when pre-focusing was forgotten or not properly performed.
So, the present invention proposes an automatic in-focus detecting device having two or more optical paths through which light is projected to a target area, while the reflections of the projected light are processed to measure the distances of two or more objects in the target area. The necessity of the aforesaid prefocusing function is removed, in U.S. patent application Ser. No. 636,590 filed Aug. 1, 1984 (corresponding to Japanese Patent Application No. SHO 58-145068.
What is essential to the invention of the above-identified U.S. patent application, however, is that the distances of the plurality of objects measured at a time are averaged and it is to this mean value that the photographic lens is to be focused. Since the object which the photographer intends to photograph with principal interest is treated with an emphasis equal to the other objects surrounding that object, there is a drawback that though the image of at least one of the objects in the same picture frame is acceptably sharp, the image of the object of principal photographic interest cannot always be of a satisfactorily sharp focus.
An object of the present invention is to eliminate the above-described drawback of the prior known device and to provide a distance measuring device for a camera having a plurality of optical paths through which light is projected to a target area as defined by the field of view of a finder of the camera with center-weighting means for putting greater emphasis on information representing the distance of one of the objects in the respective optical paths whose image lies near or at the central portion of the area of the picture frame of the camera rather than on information representing the distances of the other objects.
Other objects of the invention will become apparent from embodiments shown below.